As a technology for recording and reproducing digital data, a data-recording technology using optical disks including a magneto-optical disk as recording media is known. Examples of the optical disk are a CD (Compact Disk), an MD (Mini-Disk) and a DVD (Digital Versatile Disk). An optical disk is the generic name of recording media implemented by a disk plate made of a metallic thin plate protected by plastic to serve as media from which a signal is read out as changes in light reflected thereby.
There are two types of optical disk, i.e., a read-only type and a recordable type allowing user data to be recorded thereon. Examples of the optical disk of the read-only type are a CD, a CD-ROM and a DVD-ROM, which are known already. On the other hand, examples of the optical disk of the recordable type are an MD, a CD-R, a CD-RW, a DVD-R, a DVD-RW, a DVD+RW and a DVD-RAM, which are also already known as well. Data can be recorded onto an optical disk of the recordable type by adoption of a recording method such as a magneto-optical recording method, a phase-change recording method or a pigment-film-change recording method. The pigment-film-change recording method is also known as a write-once recording method, which allows data to be recorded onto the disk only once and does not allow other data to be recorded over the recorded data. Thus, the pigment-film-change recording method is optimum for data-saving applications. On the other hand, the magneto-optical recording method and the phase-change recording method allow other data to be rewritten. Thus, the magneto-optical recording method and the phase-change recording method are adopted in a variety of applications such as applications to record mainly a variety of contents including musical data, video data, game software and an application program.
In addition, a high-density optical disk referred to as a DVR (Data & Video Recoding) has been developed in recent-years to substantially increase the recording capacity of the disk.
A high-density disk such as the DVR has a structure including a cover layer with a thickness of about 0.1 mm in the thickness direction of the disk. In this structure, phase-change marks are recorded and reproduced under a condition of applying a combination of a laser having a wavelength of 405 nm and an objective lens with an NA of 0.85. The laser having a wavelength of 405 nm is referred to as the so-called blue laser. The structure has a track pitch of 0.32 microns and a line density of 0.12 microns/bit. In the structure, a data block having a size of 64 KB (kilobytes) is used as a recording/reproduction unit. At a format efficiency of 82%, a disk having a diameter of 12 cm allows data of an amount of 23.3 GB (gigabytes) to be recorded thereon and data already recorded there on to be reproduced.
In addition, at the same format, if the line density is increased to 0.112 microns/bit, the recording/reproduction capacity of the disk can be raised to 25 GB.
Furthermore, in a multi-layer structure including a plurality of recording layers, a considerably increased recording/reproduction capacity can be realized. In a multi-layer structure including two recording layers, for example, the recording/reproduction capacity can be doubled to 46.6 GB or 50 GB.
By the way, in a read-only disk among the various optical disks cited above, data is basically recorded in error correction block units as pits such as emboss pits created in advance on the disk. As explained above, an example of the read-only disk is a DVD-ROM. In addition, in accordance with a known conventional data format of a read-only disk, data is recorded onto a contiguous area, which does not split any error correction block. In such a format, the error correction block is used as the error correction block unit, implying that a linking area (or a buffer area) is not created between blocks.
Much like a read-only disk, data is basically recorded onto and reproduced from a recordable disk (or a recording/reproduction disk) in error correction block units.
In this case, however, taking random-access recordability into consideration, a linking area may be created between blocks.
The use of linking areas offers a merit that random accesses to blocks in a recording/reproduction apparatus can be realized by hardware less expensive than a data format without linking areas.
In a method of recording a block onto a contiguous area uninterrupted by a linking portion, on the other hand, the operation to read out data is not stable till a PLL (Phase Locked Loop) of a read clock signal gets into a steady state so that there is a danger of generating a read data error. This is because linking areas do not exist. Thus, from the random-accessibility point of view, this method has a disadvantage.
In the case of a read-only disk, however, the random-access recording does not have to be taken into consideration. Thus, linking areas are not required.
For this reason, basically, the read-only disk and the recording/reproduction disk are considered to be disks of the same type. For example, a DVD-ROM used as a read-only disk and a DVD-RAM used as a recording/reproduction disk can be considered to be disks of the same type. Other examples are the recording/reproduction disk and the read-only disk serving as the high-density disk (DVR) cited above.
Mutual reproduction compatibility is required of such disks of the same type. If there is a difference in data-arranging method (or data format) between the read-only disk having no linking areas and the recording/reproduction disk having linking areas, however, the compatibility inevitably deteriorates.
That is to say, in such a case, a reproduction apparatus designed for both the read-only disk and the recording/reproduction disk needs to have components built for the read-only disk and components for the recording/reproduction disk, and the apparatus must switch the configuration from a set of components to another set of components in dependence on which disk is used as an object of data reproduction. The components include a timing generation circuit, a synchronization circuit, other similar pieces of hardware, pieces of firmware and pieces of software.
In a word, in order to sustain compatibility, a bigger load must be imposed on the configuration of the reproduction apparatus.